#GROW

Tasty, healthy and easy to grow: Water chestnuts

Aug 15, 2022 | Written & photographs by Jason Sampson

Above: Water chestnut (Eleocharis dulcis). Photo by ricky_taylor.

There are well over 20 000 known species of edible plants in the world. Yet – due to globalisation, colonialism and the mechanisation of agriculture – only about 20 of these species provide 90% of the food needs of both humans and domestic animals.

Many of these edible plants are wild, undomesticated and not really suitable for production. Yet there are dozens of domesticated or semi-domesticated crop species in Africa that can be grown easily and productively by smallholders. These are known as orphan crops – or crops that aren’t perhaps well known and aren’t traded internationally.

These crops can be beneficial to farmers:

– They help to increase the food variety and security of the farmer’s family and livestock.

– They also help the grower to access a market in specialty, health food or ethnic markets without competing with large, established farms.

That’s why these plants can, and should, be seriously considered in a more ecologically sensitive, small-scale farming community.

One such example of an orphan crop species suitable for small-scale farming is the water chestnut (Eleocharis dulcis).

Above: Freshly harvested water chestnuts on the left, with true chestnuts, Castanea sativa on the right.

This species is better known in the East, where it is grown in rice paddies as a companion plant to the staple, and used in multiple recipes and food types from curries to stir fries. It also grows wild along the eastern parts of South Africa, particularly KwaZulu-Natal, and all through Tropical Africa.

It’s not known if the species was ever cultivated as a crop in Africa, but it would without a doubt have been known as a forage food to traditional peoples within its range, where it grew along riverbanks, lakes and pans.

The name “chestnut” might sound like the crop is some kind of tree. But water chestnut is an unassuming grass-like plant with hollow, cylindrical leaves and a spreading habit under ideal conditions. The edible part of the crop are its tubers which are visually very similar to true chestnuts and have a sweet, coconut-like taste and texture.

 Above: Water chestnuts can be grown in old metal baths, in this instance, as part of a hobby growing setup. Around 500 to 1 000 chestnuts can be produced in such a setup – perfect for one family’s use.

This is an incredibly productive crop, particularly given the minimal input needed for growth. The plant’s needs are simple: waterlogged conditions, good soil and full sun. And by adding nitrogen containing fertiliser you can increase yields even more.

It can even grow in stagnant water, so you can cultivate it in containers such as baths or modified flow-bins. Unsurprisingly the plant also lends itself perfectly to aquaponics!

How to cultivate water chestnut

Plants are grown from fresh tubers which are planted in early spring. The tubers are very hardy, and often sprout in August with warmer weather. From September to March you only need to feed the soil every 6-8 weeks with fertiliser containing nitrogen.

Although this is an aquatic plant, it can grow under irrigation for full production – but it needs to be grown in relatively stone-free soil saturated with water. The depth can be up to about 5cm, but it’s not necessary to have standing water around the plant’s crown, where the root and the stem meet. The largest tubers are produced in the top 30-50cm of soil.

Above: The first sign that harvest can begin.

There’s a secret to achieving full production

Simply take advantage of the fact that the plant spreads like a grass in the earlier part of the growing season.

Here’s a monthly breakdown of the growing process:

• September to December: Spend this time allowing the water chestnut to spread to fill an area.
• January to March: Allow the plant to become as dense as possible in that space.
• April and May: The plant forms the winter survival tubers, which are the largest and most succulent.
• The plant’s foliage dies down with the first frosts, and harvesting can begin.

Productivity in mass plantings can approach or exceed that of potatoes – roughly 40 tons per hectare. The best planting density for maximum production under normal conditions is 6-8 tubers per m².

Don’t split your plants when growing. Maximum production is a result of interaction between surface area covered and density of the final clump. Once planted at the optimal starting density, let the plants grow until harvest season. They grow so thickly they seldom need weeding.

 Above: Freshly harvested chestnuts ready for use.

Save your seeds for the following spring

For propagation purposes, the fresh tubers from which the plants are grown keep best in damp soil. Always leave a section of your growing area unharvested with tubers in place, saved for replanting in spring.

You can also supply tubers packed in wet coir (from the inner shell of the coconut) in the winter months. These are best planted soon after arrival.

How to enjoy your water chestnuts

You need to peel your water chestnut tubers before using them. But they can be eaten raw, boiled, fried or dried and made into a flour. The tubers are extremely popular in Chinese cuisine and keep their crunchy texture when cooked.

There are a million ways to use them, from gluten-free pizza base recipes to traditional stir-fries. They can also be used as a potato substitute, adding a sweet, coconut-like taste to any meal. I prefer them sliced when I use them fresh, as the crunchy texture is novel in a stew.

Above: The “chestnut” name makes a lot of sense when the tubers are peeled for use. The flesh is white, dense and crunchy with a distinct coconut flavour.

A step-up from the canned product

There are not many opportunities to buy fresh water chestnut in South Africa. In fact, most of the local demand is filled with canned tubers, which cannot compare with the fresh product. You’ll likely find them at Chinese grocers and delicatessens, amongst others. And the opportunity exists for a range of value-added produce, such as water chestnut flour or frozen chestnuts.

Few crops can produce as well on limited space, so I can highly recommend it if you have space to incorporate this crop into your growing – whether in ponds, dams or suitably modified large containers.

One last word of warning: Ducks and geese will uproot and eat any tubers they can find. So to protect both the water chestnut and the waterbirds, put suitable protection in place, such as chicken wire over your grow beds.

For more information on this, or other orphan crops, please contact Jason Sampson at jason.sampson@up.ac.za